1. Field of the Invention
The present invention is generally related to the field of orthopedic prostheses, and, more particularly, to a rotating/non-rotating tibia base plate/insert system.
2. Description of the Related Art
The two largest and longest bones of the human body, the femur and tibia, meet at a person's knee. The tibia is situated at the front and inner side of the lower leg. The head of the tibia is large and expanded on each side into two eminences, the tuberosities. These eminences form two smooth concave compartments or surfaces which articulate with the condyles of the femur. The medial condyle is more prominent anteriorly and broader both in the anterior-posterior and transverse diameters than the lateral condyle. Accordingly, the lateral articular surface of the tibia is longer, deeper and narrower than the medial articular surface of the tibia. The medial articular surface is broader, more circular, and concave from side to side. The anterior surfaces of the tuberosities are continuous with one another, forming a single large surface which is somewhat flattened. Posteriorly, the tuberosities are separated from each other by a shallow depression for the attachment of ligaments. The medial tuberosity presents posteriorly a deep transverse groove for the insertion of a tendon.
Because of aging and disease, the articulating surfaces of the knee may degrade. To treat certain pathologies, it has become common to attach a prosthetic device to the femur and a prosthetic device to the tibia. The tibia prosthesis typically comprises a base plate that is affixed to an upper, resected surface of a tibia and an articulating surface or insert which pivots about an axis within the medial condylar compartment. Tibia prostheses commonly comprise metal base plates with polyethylene articulating surfaces mounted thereon. To accommodate the range of motion of the human knee, either the femoral condyles or a femoral prosthesis rocks against the articulating surface of the tibia prosthesis.
There are many variations that a surgeon must deal with when installing a prosthetic knee assembly. For example, due to a variety of factors, the loadings exerted on an artificial knee joint may vary greatly from person to person. Such variations may be the result of physical variations in the structure of patient's knee, previous injuries, weight, etc. In some cases, it may be desirable that the tibia insert rotate relative to the tibia base plate. It is believed that such rotation allows the artificial knee to absorb some variable loadings produced on the knee joint by the patient during everyday activities. Moreover, allowing the tibia insert to rotate relative to the tibia base plate may enable such a prosthetic system to be used on a vast variety of patients. However, in some cases, it may be desirable to prevent the tibia insert from rotating relative to the tibia base plate. For example, if the various ligaments that support the knee are weak or have been previously damaged, allowing rotation of the tibia insert relative to the tibia base plate may create an unstable knee. In a worst case scenario, allowing such rotation may lead to failure of the knee joint under some loading conditions.
In view of the foregoing, it would be desirable for a surgeon to have greater flexibility as it relates to deciding whether to use a rotating or a non-rotating tibia insert on a tibia base plate. However, the decision to use a rotating or non-rotating insert may not be finally made until some point during the process of the surgery. That is, the final decision may be based upon an inspection of the surrounding ligaments and other factors that may lead the surgeon to decide on a rotating or a non-rotating tibia insert. As a result, hospitals maintain inventories of both rotating and non-rotating insert/tibia base plate combinations to accommodate both situations. Additionally, in some cases, it may be desirable or necessary to go from a rotating tibia insert to a non-rotating insert and vice versa. For example, a patient may originally obtain a prosthetic knee system with a tibia insert that rotates relative to the tibia base plate. Over a period of time, it may be desirable to have that patient use a prosthetic knee system in which the tibia insert does not rotate relative to the base plate. With prior art systems, this would typically involve major surgery to remove the existing insert/base plate system and replace it with the other type of insert/base plate system, i.e., to go from a rotating system to a non-rotating system. Obviously, such situations involved major surgery, which patients might be reluctant to endure. Thus, patients would continue to use the previously obtained insert/base plate assembly despite the fact that a better prosthetic knee assembly may be available.
The present invention is directed to various devices and methods for solving, or at least reducing the effects of, some or all of the aforementioned problems.